1. Field of the Invention
The present invention generally relates to printhead assembly apparatus used in ink jet printers, and more particularly relates to the design, manufacture, and assembly of orifice plates for such printhead assemblies.
2. Description of Related Art
A conventionally fabricated printhead assembly for an ink jet printer typically includes a piezoelectric ceramic body portion through which a spaced apart series of parallel ink receiving chambers or cavities extend from the front end of the body to its rear end. The open chamber ends at the rear end of the body are suitably communicated with the interior of an ink reservoir to receive ink therefrom, and an orifice plate, which is comprised of a dissimilar material such as a polymer, is secured over the open front end of the body using a generally planar layer of high strength adhesive material. A spaced series of ink discharge orifice openings are formed through the orifice plate, and are aligned with and positioned over the open front ends of the body chambers.
Because of the small size of these printhead bodies and orifice plates, the plate is applied to the printhead using a manual assembly fixture and aligned under a microscope. This aspect increases the cost and time it takes to manufacture such devices. The orifice plate and the printhead body are typically secured together with an adhesive. The adhesive that is used to secure the orifice plate to the printhead body is "activated" or cured by subjecting the printhead assembly to high temperatures. When bonded, the assembled printhead is removed from the oven, allowed to cool and removed from the assembly fixture. Since the body portion and the orifice plate of these conventional ink jet printhead assemblies are typically constructed from dissimilar materials, they have differing thermal coefficients of thermal expansion. As such, several problems can arise during the fabrication of these conventional printheads.
For example, because of the differing coefficients of thermal expansion between the materials, the ink discharge orifices of the orifice plate can become misaligned with the ink receiving chamber in the printhead body portion when the printhead assembly is subjected to the high temperatures necessary to cure the adhesive properly. Since the orifice array and its features are extremely small, with the orifice holes being generally in the range of 0.0001 to 0.002 inches in diameter, the dimensional tolerances on the size and location of these features are equally small--along the order of 0.00004 of an inch. Therefore, any misalignment that may occur during the curing process can have a detrimental effect on the quality and the performance of the ink jet printhead.
Additionally, the conventional adhesives, or other materials that may be used to attach the orifice plate to the body portion, must also act as a sealing gasket to seal the printhead assembly and prevent ink from leaking between the channels or various segregated areas of the printhead. Unfortunately, however, the strong solvent nature of most inks chemically attacks many common adhesives, thereby weakening the adhesive and causing structural failure and leakage. Furthermore, after the adhesive is applied to the body portion and the orifice plate is put in place, the adhesive may seep into and plug the ink receiving chambers and the orifice holes during the assembly process.
Therefore, it can readily be seen that there is a need in the art for an orifice plate and method of manufacture thereof that will provide an orifice plate that can be easily and properly aligned with the body portion and one that will prevent the adhesive from plugging the ink receiving chambers and the ink discharge orifices. The present invention provides an apparatus and method that addresses these needs.